Engine rebuild questions

17th May 2015, 18:34

Recently got a turbo vts but the car wouldn't start stripped the head of it yesterday and the valves are bent so getting a new head rebuilt to put on the car.

Have a thread on here if you need to get any more information on car.

The car is running a full jp4 conversion so have some queries about a rebuild after looking about online I feel would be worth me giving it a go.

The car was running standard Pistons, rods and bolts with a 1.9 head gasket.

Looking to run the power it was before 250bhp and hopefully get some more out of it once updated engine back in.

I'm looking at getting forged Pistons would I be best getting the standard bore of 78.5 or slightly larger ?

The new head will be skimmed so what size gasket would I be best to go for to get the best compression ? (I'm I correct in thinking I need to wait until I know how much has been skimmed off he head)

I see the arp bolts needs a modification is this the same on the jp4 engine ? If it is what's involved and is it something I could do myself or have to take to a specialist to do ? ( might go standard as seen some big powered cars not using arp bolts in set up)

Any help would be great thanks.

17th May 2015, 21:00

The bores will be slack or oval on a standard bore size, to do it properly you should alway go for a slight over bore for correct clearances.

Depending how much the head is skimmed it may only take 3thou to clean the surface up, 0.1mm is 4thou so wont affect it too much.

Id go arp for 250 just to be safe, you need to grind the shoulder of the bolt head to reduce the diameter to fit the flat on the conrod

22nd May 2015, 18:17

Give it a hone first dont just drop some pistons in a standard bore. Not on a car asking double its std output.

I am sure gmc motorsport will be happy to do the hone and then you buy pistons to suit. They will even supply.